1. Field of the Invention
The present invention relates to a focus detection device, a focus detection method, and an image pickup apparatus.
2. Description of the Related Art
There is a known focus detection device that detects a focus adjustment state of an imaging lens by receiving a first image formed with a light flux passing through one of two pupil regions of the subject imaging lens and a second image formed with a light flux passing through the other pupil region by using a solid-state image pickup element, and calculating a shift amount between the first image and the second image (see Japanese Unexamined Patent Publication No. 2007-011314, for example).
However, the conventional focus detection device uses a solid-state image pickup element of CMOS type. Focus detection pixels arranged in a transverse direction of an image capturing screen is the same as a direction of a signal read line of the CMOS image pickup element, but the focus detection pixels arranged in a direction other than the transverse direction of the image capturing screen, such as a longitudinal direction of the image capturing screen, is different from the direction of the signal read line of the CMOS image pickup element. As a result, there is the problem that synchronism in charge storing time cannot be maintained among the focus detection pixels.
Therefore, if there is movement in an image while charge storing is performed on the focus detection pixels arranged in a direction other than the transverse direction of the image capturing screen, image shift is caused between the first image and the second image due to the image movement. As a result, the image shift amount between the first image and the second image cannot be accurately calculated, and the focus detection accuracy is degraded.